Generally circuit breakers utilize a contact arm assembly comprising moveable contacts attached to the contact arms and stationary contacts attached to a line terminal and in some cases utilize several pairs of moveable and stationary contacts per phase. Usually one of the contacts in each pair is a fixed or stationary contact, while the other contact is a movable contact coupled to the operating mechanism of the circuit breaker. When operational, the stationary and the moveable contacts are closed and touch at the contact pads of the contacts. In the closed condition, the contact pair forms a current pathway between the line and load sides of the circuit breaker.
In the field of circuit breaker design, it is desirable to provide as much protection to the consumer and their electrical equipment as possible. During a fault event, a circuit breaker must respond as quickly as possible to protect connected equipment by negating or minimizing any damage to the connected equipment. To achieve this goal, circuit breakers respond to a fault event by blowing apart the moveable and stationary contacts as a result of magnetic repulsion forces created under high current conditions such as for example, a short circuit fault event.
Although high current conditions are generally sufficient to separate the moveable and stationary contacts of the circuit breaker, slot motors have been used to increase the speed of contact arm separation and thereby enhance separation performance. Slot motors are devices that function as magnetic accelerators that enhance the separation speed of the moving contract arm, away from the stationary contact arm, and directs the resulting arc towards the splitter arc plates. By shortening the life of the arc, the amount of let through energy is reduced and the amount of potential damage to both the circuit breaker and to the connected equipment is diminished.
The slot motor is generally a device surrounding a portion of the contact arm assembly 102 and is made from a magnetically permeable material, such as steel. In the event that the circuit breaker is tripped, an arc may be formed between the contact arms assembly and then drawn out by the motion of the moving contact arm towards a series of arc plates so as to divide or split and ultimately extinguish the arc. During this separation process, the arc produces a current which electromagnetically then induces a magnetic field in the magnetically permeable material of the slot motor assembly. The induced magnetic field enhances the repulsion forces at work between the stationary and contact arms so as to more quickly separate and stretch out and extinguish the arc.
The measure of performance of these interruption assemblies in circuit breakers, is quantified in terms of the amount of let through current and let through energy is allowed during a fault event. The quicker the response, the less let through energy is allowed. As such, the speed of contact separation is an important factor in minimizing damage to the circuit breaker and damage to the connected equipment.
In the manufacture of circuit breakers, the slot motor is generally placed in close proximity to the contact arm assembly, and around the pathway of travel between the load and line side of the circuit breaker. The slot motor assembly is generally made as a separate component and distinct from the contact arm assembly, and therefore must be inserted or placed adjacent to the contact arms during circuit breaker manufacture. However, due to the increasing need for further miniaturization of circuit breakers while maintaining or enhancing its functionality, the use and manufacture of circuit breakers is becoming a greater challenge. The present invention addresses the problem by utilizing a contact arm assembly, line terminal assembly, arc plate assembly and slot motor assembly in a certain configuration and by using certain ablative materials so as to quickly extinguish an arc. Moreover, the present invention addresses the need for modularity in design and the need for ease of manufacture. This invention maximizes the usage of available space by providing as much magnetically permeable material as reasonably possible while being modular in design and by enabling components of the slot motor assembly to be easily assembled within and/or around the contact arm assembly